Hollow needle applicators

ABSTRACT

A fluid filled cartridge having a fixed needle and a piston assembly for expression of its contents is mounted inside an applicator. In order to extend the needle from the body prior to cartridge contents expression and without premature leakage of fluid therefrom, an actuator is mounted in the body to drive the cartridge forwards. This is accomplished by co-operating driving and driven parts of the actuator and the cartridge (or any carrier it may have) which are decoupled by release formations in the applicator body after the cartridge has been moved sufficiently to extend the needle. The applicator also includes provision for automatic needle retraction after cartridge contents expression. A separate inventive feature is the deformability of the piston so that force transmission to the trigger means to initiate needle retraction only occurs upon full content expression when the piston has “bottomed out” within the cartridge.

This application is a 371 of PCT/GB2003/005424 filed on Dec. 12, 2003.

FIELD OF INVENTION

This invention relates to hollow needle applicators suitable foradministering cartridged drugs etc, particularly but not exclusively ina manner assuring retraction of the needle after use.

In using the term “drugs etc” herein, there is no intention to limitapplication of this invention to drugs or medicaments as such. Thisinvention is generally applicable to any usefully injectable substanceand to injecting any appropriate receiver, whether or not that is tissueof a human or animal subject.

Suitability for use in administering drugs does, however, bring incertain constraining desiderata. One is for exceptional reliability asto accuracy of the administered quantity of drug precisely as and whereintended. Another is for minimising costs of applicators as essentiallyone-use throw-away items. Other than springs, component parts need to beindividually suited to high-speed plastics injection moulding, andcollectively suited to high-speed automated assembly.

BACKGROUND TO INVENTION

Prior proposals for such applicators include providing for needleextension as a first stage in their use, i.e. having an as-suppliedstate with the needle retracted. Cartridges supplied pre-filled with ameasured drug dose typically have fixed needles, in which case suchfirst stage involves movement of the cartridge internally of theapplicator. It is known for such movement to be by the same drive forceas serves to discharge the cartridge contents through the needle bycontinuation of such force application through and after cartridgemovement for needle extension. It is further known, in relation totypical cartridges having a piston for expression of contents, for driveforce application to rely on force transmission through incompressibleliquid contents of the cartridge to achieve the first needle extensionstage of movement of the cartridge. Examples include EP0516473, whichclearly accepts drug weepage through its needle during extension as aninevitability, and also our own earlier WO93/23098 and WO95/35126.

OBJECTS OF INVENTION

An object of this invention is to provide an applicator which does notrely entirely on transmission through cartridge contents for initialneedle extending cartridge movement so as to obviate premature contentsexpression on the way to the needle reaching desired tissue penetration.

Another object of this invention is to minimize, indeed virtuallyeliminate, ullage requirement. The term ullage is used to refer to theamount by which the cartridge has previously had to be overfilled inorder to deliver the predetermined dose because it has not hitherto beenpossible to deliver the entire contents of a cartridge. There has alwaysbeen at least a small amount remaining in the cartridge and needle afterthe piston has been displaced to its full extent, and after the needlehas automatically retracted in applicators which have such provision.

SUMMARY OF INVENTION

According to one aspect of this invention there is provided a hollowneedle applicator for administering a fluid from a cartridge which has afixed needle comprising an applicator body in which the cartridge,including its needle, is mounted, a force applying actuator mounted inthe body for movement therein to drive the cartridge or a carrier forthe cartridge forwards to extend the needle from the applicator body, inwhich respect the actuator and the cartridge, or its carrier, haveco-operating driving and driven parts, and release formation meansprovided in or on the body to release the said co-operating parts afterpredetermined movement of the cartridge to extend the needle from theapplicator.

In preferred embodiments of the invention the release formation meansare arranged to deflect the co-operating driving part of the actuatoroutwardly of the co-operating driven part of the cartridge or itscarrier. This is because preferred practical embodiments of applicatorall include means for retraction of the needle after use. This meansthat an inner region of the applicator body must be kept clear toprovide for reception, upon retraction, of piston means and thecartridge body, to which the needle is attached. In embodiments whichmight be envisaged where some form of needle protection is employed inplace of automatic retraction after use, the drive part of the actuatorcould be deflected inwardly as it is decoupled from the co-operatingdriven part of the cartridge.

The movement of the cartridge to extend the needle from the applicatormay be predetermined, or may be additionally limited, in any one or moreof three ways, namely, by full compression of a spring which will act insubsequent needle retraction and is located in a forward end of theapplicator body, by abutment of a shoulder on the cartridge with a ledgeinside the applicator body, or by abutment of a shoulder on thecartridge, e.g. where a needle holder overlies the main cartridge body,with a needle guide at the forward end of the applicator body.

In preferred embodiments, the same drive force as achieves saidpredetermined movement can thereafter continue to act in discharging thecontents of the cartridge, but does not so act relative to cartridgecontents during said predetermined movement. In other words, said driveforce advantageously has no action on and applies no force toin-cartridge means (typically of piston type) for discharge pressuringof cartridge contents until positive releasing of the co-operatingdriving and driven parts of the actuator and cartridge, respectively,takes place.

Suitable driving and driven parts can be provided by extensions from theactuator and from the cartridge beyond its occupation by its contents(or from any carrier for such cartridge), respectively. Typically suchextensions will be oppositely directed and will co-operate by directengagement prior to positive disengagement by the release formationmeans. However, it would be possible to have indirect engagement betweenthese parts by way of some intermediate part(s), such as a rotatable,apertured drive coupling ring, which is/are movable by the releaseformation(s).

Suitable release formation means comprises at least one deflectorelement projecting internally of the applicator body at a positionaxially along the applicator body that the cartridge or its carrierreaches in said predetermined movement for needle extension.

Disengagement of the driving and driven parts can, in some embodiments,be by movement of an intermediate part, for example by part rotation ofan apertured member, such as the aforementioned drive ring or a slotteddisc, the slots of which are then brought into registration with thedriving and/or driven parts.

Preferred actuators have additional force-transmitting part(s) which areineffective until the mechanical coupling for needle extension isreleased, and which become effective to pressurise cartridge contentsonly after such release. Thus, preferred drive actuators, have twoforce-applying parts for different purposes, one for needle-extensionmovement of the cartridge and the other for discharging the contents ofthe cartridge.

Suitable force-applying parts can be in the form of different extensionsof or from the actuator, for example of axial-parallel nature relativeto the actuator and the applicator main body part accommodating theactuator, and one being radially inside the other.

Provision for discharging cartridge contents is preferably inconjunction with provision of means for achieving automatic needleretraction after such discharge. This further means advantageously alsoincludes releasable mechanical coupling between the other force-applyingpart(s) of the actuator and a piston of the cartridge. Moreover, it canbe particularly advantageous for the related actuator extension asdriving part and the piston rod as driven part to be relatively entranteach other at coupling release.

Positive release of this coupling is advantageously triggered bydeformation of the cartridge piston when it reaches the end of thecartridge at the end of intended contents discharge. This necessitatesthe cartridge piston being formed of suitable deformable material. Also,at the end of contents discharge there must still be substantial forceavailable from the actuator drive spring, for example up to 50% or morecompression remaining, preferably about 60%. This can assure thatsubstantially all of the cartridge contents is discharged through theneedle, so that virtually no more than needle content is undischarged.This is important for highly expensive drugs as an ullage requirementhas hitherto been the norm, i.e. the cartridge having over-fill by asmuch as 5%-10% compared with actual desired dose as delivered, which mayneed to be very accurate indeed.

The aforesaid feature, whereby needle retraction is triggered only upondeformation of the piston as it “bottoms out” within the cartridge,thereby assuring virtually entire cartridge contents discharge, is aseparate aspect of the invention. It may be employed in otherembodiments quite independently of any needle extension provision,whether by drive transmission to the cartridge (or a carrier for same)or via pressure on liquid contents of the cartridge.

Thus, according to a second aspect of this invention there is provided ahollow needle applicator for administering a fluid from a cartridgewhich has a fixed needle comprising an applicator body in which thecartridge is mounted, a piston assembly located within the cartridge andslidable therein to discharge the fluid contents of the cartridge viathe needle, a force applying actuator mounted into the body and havingat least one force transmitting part which provides a coupling with thepiston assembly effective to displace the piston assembly within thecartridge to discharge contents of the cartridge, provision forautomatic needle retraction after cartridge contents dischargecomprising spring means arranged within a forward portion of theapplicator body to act between the applicator and the cartridge to whichthe needle is fixed, and means for release of the coupling between theforce transmitting part or parts of the actuator and the pistonassembly, characterised in that the piston assembly comprises adeformable piston, a piston rod which transmits force to the piston fromthe actuator and triggering means which is movable by the piston, whendeformed into the end of the cartridge, to release the coupling betweenthe force transmitting part of parts of the actuator from the pistonassembly and bring about needle retraction.

Release of the aforesaid force-transmitting relation between the secondactuator extension and the cartridge piston rod may be by deflection fordirectly engaging parts or by movement of an intermediate member fromdrive-transmitting blockage to unblocking of at least some of thedriving/driven parts concerned, again as exemplified by use of anapertured drive ring or slotted disc.

One suitable length-shortening provision comprises a piston rod withdriven coupling extension parts designed to be deflected away from eachother or outwardly for coupling release and a triggering rod slidable inbore through the piston rod to spread those parts when the piston isdeformed at reaching the end of the cartridge.

Another suitable length-shortening provision comprises a piston rod withdriven coupling extension parts to be deflected towards each other orinwardly for coupling release and a triggering collar slidable about thepiston rod to clench those parts when the piston is deformed at reachingthe end of the cartridge.

BRIEF DESCRIPTION OF DRAWINGS

Exemplary specific embodiments of this invention are shown in anddescribed relative to the accompanying diagrammatic drawings, in which:

FIG. 1 is an axial sectional view of a first embodiment;

FIGS. 2A to C are related detail scrap views;

FIGS. 3A to D show stages of operation of the first embodiment;

FIGS. 4A to D are cross-sectional views at A to D of FIGS. 3A to D;

FIG. 5 is an axial sectional view of a second embodiment;

FIGS. 6A to D show stages of operation of the second embodiment;

FIGS. 7A to D are cross-sectional views at A to D of FIGS. 6A to D; and

FIGS. 8A to C illustrate details for rotational drive coupling andrelease, in a third embodiment of the applicator of the invention.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS

In the drawings, referring first to FIGS. 1 and 2A to D, an applicator100 is shown as having a hollow generally cylindrical body comprising amain portion 101A and a relatively short forward portion 101B of reducedsection, the whole body 101A, B being designed for being moulded in onepiece. The applicator body may have a cross-sectional shape other thancircular. For example, oval or polygonal or irregular shapes are equallyfeasible.

The main body portion 101A terminates in an open end 102 which is shownwith a slight flare beyond an internal peripheral groove 103 and with anexternal thickening grip formation 104 below an end bead 105. Thereduced section forward portion 101B terminates in a returned end face106 which is shown centrally apertured at 106A for passage of a hollowneedle 107 through an inwardly flared re-entrant portion 108. The latterretains a needle shield 109 that in use is typically made of non-curingelastomeric material and pierced by extension of the needle 107.

The needle 107 and the shield 109 are shown fitted to a reduced end 110Bof a hollow generally cylindrical cartridge which has a main portion110A slidable in the applicator body 101 including its forward portion101B. The reduced cartridge portion 110B is shown as having a slightlyenlarged end to aid retention of the needle shield 109.

The main cartridge portion 110A has pre-loaded contents 112 and a piston111 therein and it extends (110E) beyond the full contents-accommodatingposition of the piston 111. An alternative to the cartridge being soextended (110E) would be for such extension to be of a carrier or holderfor a standard cartridge. The piston 111 is of deformable material aswill be described in relation to maximising expression of cartridgecontents 112. An exterior shoulder 110S between the main and reducedportions 110A, B of the cartridge is acted upon by a compression spring113 which is seated at 114 about the re-entrant portion 108 of theforward body portion 101B. This compression spring 113 can furthercompress to allow cartridge movement up to abutment of the cartridgeshoulder 110S (or part of a cartridge carrier/holder) against aninternal ledge 101L of the applicator body portion 101B as will bedescribed for needle extension.

The internal groove 103 around the other end 102 of the main bodyportion 101A aids secure location by external ribbing 115R of a plug 115which incorporates a releasable capture provision 118 for an actuator120. The illustrated capture provision 118 is operative relative to aneck reduction groove 121G in an end extension 121 of the actuator 120,conveniently by way of a slider part 119 with a key-hole aperture 119Kthat holds or releases the actuator extension 121 according to sliderposition controlled by a knob or button 119S. However, a slideroperating knob or button as illustrated at 119S is neither essential norparticularly preferred for operation of an applicator in accordance withthe invention. An arrangement for push-operation from a side of the bodypart 101A short of its end may well be preferred for at least somepractical implementations.

The capture provision 118 shown includes a plug having an inwardextension 118E. This provides recessed seating 122S for a head part 122of the actuator 120 below the neck-grooved part 121 and also outerseating 125S for an actuator drive spring 125 which acts on outwardflanging 124F of a main actuator part 124 extending from the head part122.

It will be appreciated that the drive spring 125 cannot move theactuator 120 until the extension part 121 is released from the captureprovision 118.

The objectives of such released movement of the actuator 120 includesfirst to move the cartridge (110A, B) for needle extension withoutreliance on application of force to the cartridge piston 111 thus not onforce transmission through the cartridge contents 112, i.e. withoutinvolving either static friction of the piston or hydraulic lock, andsecondly, only after such needle extension, to apply force to thecartridge piston 111 in pressuring the cartridge contents 112 fordischarge through the needle 107.

For achieving the first objective, FIG. 1 shows a releasable mechanicalcoupling between a driving part in the form of extensions 126 from theflanging 124F of the main actuator part 124 and a driven part in theform of the extension 110E of the cartridge (110A, B) beyond the fullpre-load position of the cartridge piston 111.

The illustrated releasable coupling mechanism involves the ends 126E ofthe actuator coupling extensions 126, which are, as shown, inclinedradially inwardly for force-transmitting engagement with the registeringcartridge extensions 110E, being releasable from such drive forcetransmitting engagement by radially outward deflection. This releasingdeflection involves positive deflecting action by release formations inthe form of deflector elements (also termed triggering extensions) 128which project internally of the main body part (101A, B) of theapplicator. Specifically, these triggering extensions 128 are axiallyparallel projections from the reduced section of the forward bodyportion 101B into the main body portion 101A immediately around the maincartridge part 110A, thus also having advantageous sliding and locatingrelation therewith.

Feasible variations on this releasable coupling (126E/110E) include thecartridge (110A, B) being provided in a carrier which has the couplingextensions. Additionally or alternatively the radially relatively inwardand outward relationship between the coupling extensions 126E and 110Ecould be reversed, i.e. the cartridge or carrier coupling extensions110E could be outward of the actuator coupling extensions 126, 126E andthe triggering extensions 128 could be radially located to suit.Additionally or alternatively the release deflection could be of theends of the cartridge or carrier coupling extensions 110E, either aloneor conjointly with some end deflection of the actuator couplingextensions 126.

FIG. 2A shows the deflectable ends 126E of the actuator couplingextensions 126 as having a hinge notch 126N shown open in FIG. 2A butclosed in FIG. 1, and part-bifurcation slotting 126S and tapering 126Tto aid co-operation with end tapering 128T of the triggeringextension(s) 128. The slotting 126S will accommodate the triggeringextensions 128.

As should be apparent from FIG. 1, but see also FIGS. 3A/B, the needle,extending movement of the cartridge 110A, B is accompanied bycompression of the retraction spring 113, and is by an amount pre-set toachieve abutment of the cartridge shoulder 110S and the internal ledging101L of the forward body portion 101B. Strict coincidence betweenachieving this abutment and completing positive release action of thetriggering extensions 128 is desirable but is not essential.

One way to assure mechanical coupling right up to cartridge-arrestingabutment is to use a two-stage releasable mechanical coupling, having afirst stage along the lines described above but with another drivecoupling element that is not so positively disengaged but will disengageautomatically when the cartridge is finally arrested by abutment. Suchother coupling element will have a load-bearing requirement less thanthat of the positively disengaged elements as the drive spring will beextended near to its maximum for needle extension.

FIG. 2B and 2C in its various components shows a two-stage releasablemechanical coupling with an additional independently deflectableextension leaf 126A between those 126E positively deflected by spacedparallel triggering extensions 128A, B and with its end shaped for lesspurchase on co-operating coupling extension 110E so as to deflect fordecoupling simply by reaction to arrest of the cartridge 110. Forillustrative purposes only, FIGS. 2B and C show undeflected couplingengagements to the left and deflected dis-engagements to the right.

The second actuator objective, namely operation of the cartridge piston111 to discharge the cartridge contents 112 through the needle 107, alsoinvolves a releasable force-transmitting coupling, this time associatedwith a cartridge piston rod 131. Specifically, the engagedforce-transmitting state of this coupling 130 is between deflectablecoupling extensions 131E of the cartridge piston rod 131 and couplingextensions 132E of a centrally extending actuator part 132. The pistonrod 131 is hollow about a trigger rod 133, which goes to a point at itsrear end. This trigger rod 133 can slide axially in the hollow pistonrod 131 to deflect the coupling extensions 131E of the piston rod 131 inrelease of the mechanical coupling 131E/132E. This release action isdependant on the cartridge piston 111 reaching the end of the internalcontents-accommodating space of the cartridge (110A, B) and beingdeformed there to move the trigger rod 133 as well as assure maximaldischarge of the contents 112 of the cartridge 110A, B.

The coupling extensions 131E can be inverted forms of what is shown inFIGS. 2A to 2C including bifurcation if the trigger rod 133 islongitudinally ribbed, ridged or splined, i.e. with any such ribbing,ridging or splining accommodated in such bifurcations.

What is shown in FIG. 2A is well suited to embodiments with three orfour angularly spaced sets of inter-acting coupling extensions for eachreleasable mechanical coupling, typically equi-spaced about theapplicator axis. However, two each is practical, as in FIGS. 4A to D tobe described later.

Sequential operation of the applicator of FIG. 1 is shown in FIGS. 3A toD. In the as supplied state in FIG. 3A the actuator 120 is held by thecapture/release provision 118, the actuator drive spring 125 fullycompressed, the mechanical coupling 126E/110E engaged and the releasablemechanical coupling 131E/132E also engaged. In the released state shownin FIG. 3B the actuator 120 has been moved by the drive spring 125 tocomplete needle extending cartridge movement at abutment of thecartridge shoulder 110S with the body ledging 101L, and release of theactuator/cartridge drive coupling 126E/110E by the triggering extensions128. In FIG. 3C discharge of the cartridge contents 112 has taken placewith the mechanical coupling 131E/132E still engaged up to deformationof the piston 111 and release of the coupling 131E/132E by the triggerrod 133 deflecting the piston extensions 131E. Finally in FIG. 3Dretraction of the discharged cartridge 110A, B and its needle 107 fullyinto the body part 101A, B has taken place. The coupling extensions 132Eof the actuator 120 have accordingly entered the cartridge piston space131S about the trigger rod 133, and the cartridge or carrier couplingextensions 110E as well as the trigger extensions 128 have passingthrough an actuator flange 124F and into an actuator slot 124Y (startedat FIG. 3C stage).

The cross-sections of FIGS. 4A to D show two-element releasablemechanical couplings 126E/110E and 131E/132E, the elements being indiametric relation and with main body guidance by way of ribs andgrooves 101G/126R. FIG. 4C shows the coupling extensions 126E deflectedinto release compared with FIG. 4A, and FIG. 4D shows the actuator part132 entrant the cartridge or carrier extension 110E compared with FIG.4B.

Turning to the second embodiment, as shown in FIG. 5, its differencescompared with FIG. 1 lie in the structure for realising the secondactuator objective, namely the releasable mechanical coupling involvedin cartridge discharge. The actuator 500 is therefore the same as theactuator 100 of FIG. 1 except for its cartridge discharge piston rod 531being located within a bottom-flanged or inverted top-hat sectiontriggering collar 533. This collar has an axial through-bore 533B andthere is a space 533S outside its reduced section upstand 533U foraccommodating a tubular extension 532E of the actuator 532 after releaseof the mechanical coupling which has brought about cartridge contentsdischarge.

The releasable mechanical coupling shown involves co-operation between afree end rim 532R of the tubular actuator extension 532E and splayedcoupling extensions 531E from the inner end of the piston rod 531. Thepiston rod 531 is able to slide in relation to the collar 533, in itsbore 533B, during deformation of the piston 511 when it reaches the endof the cartridge 510. This relative sliding (531/533) results in thecollar upstand 533U acting as a trigger ring to bring about release ofthe coupling 531E/532E, specifically by radially inward deflection ofthe extensions 531E of the piston rod 531, as is apparent in FIG. 6C.

The coupling extensions 531E of the piston rod 531 are partially splitto present longer radially inward extensions 531F for guidance of theend of the actuator tubular extension 532. An alternative would be forthe ends of each of the coupling extensions 531E to be stepped.

The releasable coupling 531E/532E is of an essentially similar nature tothat already disclosed in our above mentioned PCT applications.Sequential automatic operation of the applicator 500 is believed to beapparent from the stages shown in FIGS. 6A to D, in which referencenumerals for corresponding parts have been advanced by 400 compared withFIGS. 1 to 4 other than the specific differences noted above for FIG. 5.

As illustrated for the applicator embodiments of FIGS. 1 to 7, it isfeasible and advantageous for the radially offset drive couplingextensions 126, 526 with deflectable ends and their co-operatingdeflector elements 128 which bring about release after needle extensionto be accommodated compactly after such release within consecutiveradial spaces inside the coupling extensions 126/526E and the outsidetriggering extensions 128. Likewise the elements 131/132E (FIGS. 1 to 4)released at cartridge discharge and the elements 532E/533U of FIG. 5 areaccommodated in consecutive radial spaces.

Such radial or transverse compactness can be enhanced to the extent ofeffectively “losing” one of those thicknesses if the co-operatingelements are out of angular registration and their decoupling relies onrotation of an apertured interposed ring, as shown by way of example inFIGS. 8A, B.

In FIG. 8A, a drive coupling ring 850 has outer angularly spacedapertures 851 and 852 and inner angularly spaced apertures 853. Theapertures 851 have side tapers 851T which in use co-operate with sidetapering 828T of triggering extensions 828 to rotate the ring 850 to aposition where the apertures 851 afford full clearance to the triggeringextensions 828. The apertures 852 lie next to drive engagement positions854 for mechanical coupling extensions 826 from a spring-driven driveactuator (not shown). This drive engagement will prevail until rotationof the ring 850 by the triggering extensions 828 brings the apertures852 into clearance registration with the drive coupling extensions 826.The inner apertures 853 are next to engagement positions 855 for drivenmechanical coupling extensions 810E from a cartridge or carriertherefore (not shown). These apertures will afford full clearance forthe driven coupling extensions after rotation of the ring 850 by thetriggering extensions 828, to allow a retracted state equivalent to thatof FIG. 3D, i.e. overlapping the length of the drive spring engaged partof the actuator 120 without re-compression of the actuator drive spring125. Although not shown in FIG. 8, the drive spring 125 could engage thering 850 at the outer apertured part of its width.

Rotational drive coupling and release is equally feasible for the secondmechanical coupling operative for retraction of the discharged cartridgeand its needle. Equivalents to outer aperturing 851/852 of FIG. 8A wouldsuffice where the actuator drive coupling extensions and releasetriggering extensions concerned are angularly spaced at the same radialpositions. FIG. 8C shows a drive coupling ring 860 where the triggeringextensions 831 are radially inside the actuator drive coupling extension832E, and outer and inner apertures 862, 861 correspond thereto,respectively. The extensions 831 can be upstands from a collar 831C. Asalready described for the outer apertures of FIG. 8A, rotation of thering 860 is by mutual engagement of tapers 831T/861T and results in fullclearances 831/861 and 832E/862.

1. A hollow needle applicator for administering a fluid from a cartridgewhich has a fixed needle, said applicator comprising an applicator bodyin which the cartridge is mounted; a piston assembly located within thecartridge and slidable therein to discharge the fluid contents of thecartridge via the needle; a force applying actuator mounted into thebody and having at least one force transmitting part which provides acoupling with the piston assembly effective to displace the pistonassembly within the cartridge to discharge contents of the cartridge;and a provision for automatic needle retraction after cartridge contentsdischarge comprising spring means arranged within a forward portion ofthe applicator body to act between the applicator and the cartridge towhich the needle is fixed; wherein the piston assembly comprises adeformable piston, a piston rod which transmits force to the piston fromthe actuator, and a triggering means which is movable by the piston,when deformed into the end of the cartridge, to release the couplingbetween the force transmitting part or parts of the actuator and thepiston assembly and bring about needle retraction; and wherein thepiston rod is hollow and has driven extension parts which co-operatewith the force transmitting part or parts of the actuator and aredeflectable away from each other upon release from said forcetransmitting part or parts and the triggering means comprises a rodwhich is slidable within the hollow piston rod to deflect said extensionparts.
 2. A hollow needle applicator for administering a fluid from acartridge which has a fixed needle, said applicator comprising anapplicator body in which the cartridge is mounted; a piston assemblylocated within the cartridge and slidable therein to discharge the fluidcontents of the cartridge via the needle; a force applying actuatormounted into the body and having at least one force transmitting partwhich provides a coupling with the piston assembly effective to displacethe piston assembly within the cartridge to discharge contents of thecartridge; and a provision for automatic needle retraction aftercartridge contents discharge comprising spring means arranged within aforward portion of the applicator body to act between the applicator andthe cartridge to which the needle is fixed; wherein the piston assemblycomprises a deformable piston, a piston rod which transmits force to thepiston from the actuator, and a triggering means which is movable by thepiston, when deformed into the end of the cartridge, to release thecoupling between the force transmitting part or parts of the actuatorand the piston assembly and bring about needle retraction; and whereinthe piston rod has driven extension parts which co-operate with theforce transmitting part or parts of the actuator and are deflectabletowards each other upon release from said force transmitting part orparts and the triggering means comprises a collar slidable about thepiston rod to deflect said extension parts.
 3. A hollow needleapplicator for administering a fluid from a cartridge which has a fixedneedle, said applicator comprising an applicator body in which thecartridge is mounted; a piston assembly located within the cartridge andslidable therein to discharge the fluid contents of the cartridge viathe needle; a force applying actuator mounted into the body and havingat least one force transmitting part which provides a coupling with thepiston assembly effective to displace the piston assembly within thecartridge to discharge contents of the cartridge; and a provision forautomatic needle retraction after cartridge contents dischargecomprising spring means arranged within a forward portion of theapplicator body to act between the applicator and the cartridge to whichthe needle is fixed; wherein the piston assembly comprises a deformablepiston, a piston rod which transmits force to the piston from theactuator, and a triggering means which is movable by the piston, whendeformed into the end of the cartridge, to release the coupling betweenthe force transmitting part or parts of the actuator and the pistonassembly and bring about needle retraction; and wherein the piston rodhas driven extension parts which co-operate with the force transmittingpart or parts of the actuator and are coupled thereto by way of a drivecoupling ring which is provided with spaced apertures and is rotatableby the triggering means to allow passage of the force transmitting anddriven extension parts through these apertures.